In this chapter we specifically address the issue of multiple case studies and offer a new basis for case embeddedness: time. The approach combines the concept of periodisation (Jessop, 1990) with the work of Pawson and Tilley (1997) which offers a practical realist approach to evaluation based on context-mechanism-outcome (CMO) configurations. A number of methodological benefits are identified including increasing the number of cases available and providing the possibility to explore the role of different contexts on the outcomes of the processes involved. The approach is demonstrated using case studies from a study of the impact across different industries of the banning of chlorofluorocarbons (CFCs).